Waveguide configuration

ABSTRACT

A waveguide configuration comprising a core, a first cladding, a second cladding, and a buffer. The core includes an index of refraction and an acoustic shear velocity. The first cladding extends about the core and has an acoustic shear velocity which is less than that of the core and an index of refraction which is less than the core. The second cladding extends about the first cladding. The second cladding has an acoustic shear velocity which is greater than that of the first cladding and less than the acoustic shear velocity of the core. The second cladding has an index of refraction which is less than that of an optical mode. The buffer extends about the second cladding.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/052,464 filed Feb. 7, 2005, now U.S. Pat. No. 7,209,626 which is acontinuation-in-part of U.S. patent application Ser. No. 10/766,289filed Jan. 27, 2004, now U.S. Pat. No. 7,079,749 which claims priorityfrom U.S. Provisional Patent Application Ser. No. 60/442,843 filed Jan.27, 2003, the disclosure of both of which are incorporated by referencein their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to waveguides, and moreparticularly, to a waveguide comprising a particular construction so asto suppress the SBS effect. It will be understood that a waveguide islikewise commonly referred to as fiber optic cable, or fibers.

2. Background Art

The use of waveguides in various industries such as telecommunicationsand lasers, among others, has been steadily increasing. While theability to send optical signals through waveguides is well known in theart, certain phenomena have been observed. In particular, one effectthat has been observed is the Stimulated Brillouin Scattering (SBS)effect. SBS is an important example of a stimulated scattering process;light scattering which occurs when the intensity of the light fielditself affects the propagating medium. This phenomenon has becomerelevant in the optical fiber industry, due to the increasing intensityrequired in optical fiber cores and the relatively long interactionlengths. SBS is one of the major limiting factors on the amount of powerthat can be transmitted via an optical fiber.

Certain prior art references have attempted to suppress the SBS effectthrough the use of waveguides which have particular constructions. Whilesome of the solutions have suppressed the SBS effect to some extent,many of these waveguides have constructions which are difficult tomanufacture on a large scale, or which are economically not feasible.

Accordingly, it is an object of the invention to overcome thedeficiencies in the prior art. For example, it is an object of thepresent invention to provide a waveguide construction which is botheconomical to manufacture and feasible to manufacture which suppressesthe SBS effect.

It is likewise an object of the invention to provide enhancedsuppression of SBS through further development and improvement of thefiber disclosed in U.S. Pat. No. 6,587,623. The entire disclosure ofU.S. Pat. No. 6,587,623 is incorporated herein by reference.

These objects as well as other objects of the present invention willbecome apparent in light of the present specification, claims, anddrawings.

SUMMARY OF THE INVENTION

The invention comprises a waveguide configuration with engineeredoptical and acoustic properties. The waveguide configuration comprises,a core, a first cladding, a second cladding, and a buffer. The coreincludes an index of refraction and an acoustic shear velocity. Thefirst cladding extends about the core and has an acoustic shear velocitywhich is less than that of the core and an index of refraction which isless than the core. The second cladding extends about the firstcladding. The second cladding has an acoustic shear velocity which isgreater than that of the first cladding and less than the acoustic shearvelocity of the core. The second cladding has an index of refractionwhich is less than that of an optical mode. The buffer extends about thesecond cladding.

In a preferred embodiment, a cross-sectional configuration of each ofthe core, the first cladding and the second cladding are substantiallyuniform along a length thereof.

In another preferred embodiment, the waveguide configuration furthercomprises a third cladding positioned between the second cladding andthe buffer. The third cladding has an index of refraction less than thatof each of the core, first cladding and second cladding.

In another preferred embodiment, the second cladding has an acousticshear velocity that is less than that of the core and an index ofrefraction that is less than that of the core.

In another preferred embodiment, the core comprises substantiallyundoped SiO₂, the first cladding comprises SiO₂ doped with F, P₂O₅, andGeO₂, the second cladding comprises SiO₂ doped with F.

In yet another preferred embodiment, the core comprises SiO₂ doped withAl₂O₃, P₂O₅, F, GeO₂ and Er, a first cladding comprises SiO₂ doped withF and GeO₂, and a second cladding comprises substantially undoped SiO₂.

In another embodiment, the core comprises SiO₂ doped with Al₂O₃, P₂O₅and Yb, a first cladding comprises SiO₂ doped with F, GeO₂, P₂O₅, and asecond cladding comprises SiO₂ doped with F and P₂O₅.

Preferably, wherein the waveguide comprises a third cladding extendingabout the second cladding, the core comprises SiO₂ doped with Al₂O₃,P₂O₅ and Yb, the first cladding comprises SiO₂ doped with F, GeO₂ andP₂O₅, the second cladding comprises SiO₂ doped with F and P₂O₅, and thethird cladding comprises SiO₂ doped with F.

In one embodiment, each of the core, the first cladding and the secondcladding include a radial thickness. The radial thickness of the secondcladding is greater than that of the first cladding. In one suchpreferred embodiment, the radial thickness of the second cladding isgreater than the combined radial thickness of the core.

In another embodiment, the radial thickness of the second cladding isgreater than that of the core.

In yet another embodiment, each of the core, the first cladding and thesecond cladding include a radial thickness, the radial thickness of thefirst cladding being greater than that of the core.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawingswherein:

FIG. 1 of the drawings is a cross-sectional representation of a firstwaveguide configuration of the present invention;

FIG. 2 of the drawings is a cross-sectional representation of a secondwaveguide configuration of the present invention;

FIG. 3 of the drawings is a cross-sectional representation of the indexof refraction and the acoustic shear velocity of an exemplary fiber ofthe present invention;

FIG. 4 of the drawings is a cross-sectional representation of the indexof refraction and the acoustic shear velocity of an exemplary fiber ofthe present invention;

FIG. 5 of the drawings is a cross-sectional representation of the indexof refraction and the acoustic shear velocity of an exemplary fiber ofthe present invention; and

FIG. 6 of the drawings is a cross-sectional representation of the indexof refraction and the acoustic shear velocity of an exemplary fiber ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible of embodiment in many differentforms, there is shown in the drawings and described herein in detailseveral specific embodiments with the understanding that the presentdisclosure is to be considered as an exemplification of the principlesof the invention and is not intended to limit the invention to theembodiments illustrated.

It will be understood that like or analogous elements and/or components,referred to herein, may be identified throughout the drawings by likereference characters. In addition, it will be understood that thedrawings are merely schematic representations of the invention, and someof the components may have been distorted from actual scale for purposesof pictorial clarity.

Referring now to the drawings and in particular to FIG. 1, a waveguideconfiguration made in accordance with the present invention is showngenerally as 10. Waveguide 10 includes core 12, a first cladding 14, asecond cladding 16 and a buffer 20. In some applications, there may be athird cladding 18 as illustrated in FIG. 2. While the various layers areshown to have substantially uniform thicknesses, it will be understoodthat the particular thickness of any layer can be varied within thescope of the present invention. In addition, it is contemplated that thewaveguide may comprise a substantially uniform cross-section along thelength thereof. Among other cross-sectional configurations, circularcross-sectional configurations, are contemplated, as are oval shapedcores or cladding (i.e., for use with optical fibers that preservepolarization).

Core 12 is shown in FIG. 1 as comprising a first material having anindex of refraction n_(core) and a certain acoustic shear velocityv_(core).

First cladding 14 extends around the core and is defined by an index ofrefraction n_(clad1) and a certain acoustic shear velocity v_(clad1).The acoustic shear velocity of the first cladding is less than that ofthe core (i.e., v_(clad1)<v_(core)). Similarly, the index of refractionof the first cladding is less than that of the core (i.e.,n_(core)>n_(clad1)).

Second cladding 16 extends around the first cladding and is defined byan index of refraction n_(clad2) and an acoustic shear velocityv_(clad2). The acoustic shear velocity of the second cladding is greaterthan the acoustic shear velocity of the first cladding (i.e.,v_(clad2)>v_(clad1)). Significantly, the acoustic shear velocity of thesecond cladding is less than the acoustic shear velocity of the core(i.e., v_(core)>v_(clad2)). In turn, the acoustic shear velocity of thesecond cladding is between that of the core and the first cladding.(i.e., v_(core)>v_(clad2)>v_(clad1)).

The overall optical mode has an index of refraction greater than thatthat of the second cladding (i.e., n_(opticalmode)>n_(clad2)). It willbe understood that the optical mode is generally confined to the portionof the waveguide that carries the vast majority of the light propagatingtherethrough. In certain embodiments, the index of refraction of thesecond cladding will be lower than that of the first cladding (i.e.,n_(clad1)>n_(clad2)). In other embodiments, the first and secondcladding may have a similar, or identical, index of refraction.

In many embodiments, the second cladding will have a radial thicknessthat is greater than that of the first cladding, and in certainembodiments, greater than both the first cladding and the secondcladding. Additionally, the first cladding in many contemplatedembodiments will have a radial thickness that is greater than that ofthe core.

Buffer 20 extends around the second cladding and, as will be understoodby those of skill in the art, imparts tensile strength and a certainflexibility to the fiber. Typical buffers of the type commonly used inconnection with waveguides are contemplated for use, such as a naturalor synthetic polymer. In certain instances, the buffer may comprise arelatively high index polymer. In other applications, the buffer maycomprise a relatively low index polymer.

In certain applications, such as telecommunications, the above-describedfiber is suitable for use. However, and as is shown in the embodiment ofFIG. 2, in association with lasers, an additional, third cladding 18 ispositioned between second cladding 16 and buffer 20. Third cladding 18includes an index of refraction n_(clad3) which is less than the indexof refraction of first cladding 14, second cladding 16 and core 12. Insome cases, the buffer and third-cladding layer may be replaced by alow-index polymer material.

A number of exemplary fibers of the present invention have beenformulated pursuant to the present invention. Table I below identifiesthe effect of various dopants on SiO₂ which forms the basis of thefollowing examples. It will be understood that the actual valuesidentified in the chart tend to vary slightly from manufacturer tomanufacturer due to variations in purification and manufacturingprocesses.

TABLE I Longitudinal Sheer Acoustic Index Acoustic Velocity VelocityDopant (% change/mol %) (m/s/mol %) (m/s/mol %) GeO₂ +0.062 −45 to −65−45 to −55 P₂O₅ +0.020 −84 −111 F −0.091 −185 −159 Al₂O₃ +0.055 +32 +9.4

The following examples describe the various exemplary fibers. Of course,the invention is not limited to the below described fibers, and thesefibers shall be deemed only as exemplary embodiments.

EXAMPLE 1

An exemplary transmission fiber has been determined based upon theabove-identified criteria. The contemplated fiber includes a corecomprising pure SiO₂ having a radius of 4.5 micrometers. The firstcladding comprises 4.1 mol % F, 1.4 mol % P₂O₅ and 1.0 mol % GeO₂ dopedSiO₂ having a radial thickness of 12.5 micrometers. The second claddingcomprises 3.1 mol % F doped SiO₂ having a radial thickness of 62.5micrometers. The buffer comprises a high index polymer.

As is shown in FIG. 3, in such an embodiment, the index of refraction ofthe core is greater than the index of refraction of the first cladding.The index of refraction of the second cladding is greater than the indexof refraction of the first cladding. In other words,n_(core)>n_(clad2)>n_(clad1). With respect to the acoustic shearvelocity, the acoustic shear velocity of the core is greater than theacoustic shear velocity of the first cladding. The acoustic shearvelocity of the second cladding is greater than the acoustic shearvelocity of the first cladding. In other words,v_(core)>v_(clad2)>v_(clad1).

EXAMPLE 2

An exemplary single clad Er doped fiber has been determined based uponthe above-identified criteria. The contemplated fiber includes a corecomprising 6.0 mol % Al₂O₃ and 0.1 mol % P₂O₅ and 0.2 mol % F and 0.1mol % GeO₂ and 1000 ppm/wt. Er doped SiO₂ having a radius of 2.2micrometers. The first cladding comprises 1.9 mol % F and 4.0 mol % GeO₂doped SiO₂ having a radial thickness of 6 micrometers. The secondcladding comprises pure SiO₂ having a radial thickness of 62.5micrometers. A high index polymer buffer surrounds the second cladding.

In such an embodiment, as shown in FIG. 4, the index of refraction ofthe core is greater than the index of refraction of the first cladding.The index of refraction of the first cladding and the second cladding issubstantially the same. In other words, n_(core)>n_(clad1)=n_(clad2).The acoustic shear velocity of the core is greater than the acousticshear velocity of the first cladding. The acoustic shear velocity of thesecond cladding is greater than the acoustic shear velocity of the firstcladding. In other words, v_(core)>v_(clad2)>v_(clad1).

EXAMPLE 3

An exemplary dual clad Yb doped fiber was determined based upon theabove-identified criteria. The exemplary fiber includes a corecomprising 1.4 mol % Al₂O₃ and 0.2 mol % P₂O₅ and 20,000 ppm/wt. Ybdoped SiO₂ having a radius of 10 micrometers. The first claddingcomprises 2.5 mol % F and 0.7 mol % GeO₂ and 9.1 mol % P₂O₅ doped SiO₂having a radial thickness of 15 micrometers. The second claddingcomprises 2.0 mol % F and 9.1 mol % P₂O₅ doped SiO₂ having a radialthickness of 150 micrometers. A low index polymer buffer surrounds thesecond cladding.

In such an embodiment, as shown in FIG. 5, the index of refraction ofthe core is greater than the index of refraction of the first cladding.The index of refraction of the first cladding and the second cladding issubstantially the same. In other words, n_(core)>n_(clad1)=n_(clad2).The acoustic shear velocity of the core is greater than the acousticshear velocity of the first cladding. The acoustic shear velocity of thesecond cladding is greater than the acoustic shear velocity of the firstcladding. In other words, v_(core)>v_(clad2)>v_(clad1).

EXAMPLE 4

An exemplary dual clad Yb doped fiber with glass third cladding wasdetermined based upon the above-identified criteria. The exemplary fiberincludes a core comprising 1.4 mol % Al₂O₃ and 0.2 mol % P₂O₅ and 20,000ppm/wt. Yb doped SiO₂ having a radius of 10 micrometers. The firstcladding comprises 0.7 mol % F and 0.7 mol % GeO₂ and 9.1 mol % P₂O₅doped SiO₂ having a radial thickness of 15 micrometers. The secondcladding comprises 2.0 mol % F and 9.1 mol % P₂O₅ doped SiO₂ having aradial thickness of 150 micrometers. The third cladding comprises 4.0mol % F doped SiO₂ having a radial thickness of 200 micrometers. A highindex polymer buffer surrounds the third cladding.

In such an embodiment, as is shown in FIG. 6, the index of refraction ofthe core is greater than the index of refraction of the first cladding.The index of refraction of the first cladding and the second cladding issubstantially the same. The index of refraction of the third cladding isless than that of the second cladding. In other words,n_(core)>n_(clad1)=n_(clad2)>n_(clad3). The acoustic shear velocity ofthe core is greater than the acoustic shear velocity of the firstcladding. The acoustic shear velocity of the second cladding is greaterthan the acoustic shear velocity of the first cladding. The acousticshear velocity of the third cladding is less than the acoustic shearvelocity of the third cladding but greater than the acoustic shearvelocity of the second cladding. In other words,v_(core)>v_(clad2)>v_(clad3)>v_(clad1).

In operation, acoustic waves are constantly radiating from the core,whether the core is acoustically guiding or not. This is the fundamentaldifference between the optical and acoustic modes and is a result of thefact that the glass behaves as a compressible fluid. The boundarybetween the first and second cladding results in a phenomenonsubstantially analogous to the total internal reflection of opticalwaves in the core. Thus, the first cladding substantially captures thesewaves, resulting in acoustic guidance. These waves are thenre-transmitted into the core, interfering with the acoustic wavesinvolved in the SBS process. This may also result in increased acousticmode coupling into the first cladding layer. These processes then giverise to a degraded overlap between the optical and acoustic fields,leading to an increase in the threshold intensity for the onset of SBS.

The foregoing description merely explains and illustrates the inventionand the invention is not limited thereto except insofar as the appendedclaims are so limited, as those skilled in the art who have thedisclosure before them will be able to make modifications withoutdeparting from the scope of the invention.

1. A waveguide configuration comprising: a core having an index ofrefraction and an acoustic shear velocity; a first cladding extendingabout the core having an acoustic velocity which is less than that ofthe core and an index of refraction which is less than the core; asecond cladding extending about the first cladding, the second claddinghaving an acoustic velocity which is less than that of the firstcladding and less than the acoustic velocity of the core, the secondcladding having an index of refraction which is less than the effectiveindex of an optical mode.
 2. The waveguide configuration of claim 1further comprising a third cladding positioned between the secondcladding and a buffer, the third cladding having an index of refractionless than that of each of the core, first cladding and second cladding.3. The waveguide configuration of claim 1 wherein the core comprisesSiO₂ doped with Al, at least one rare earth element, and at least on ofGe, P, F, and B.
 4. The waveguide configuration of claim 1 wherein thecore comprises SiO₂ doped with P, at least one rare earth element, andat least one of Ge, Al, F, and B.
 5. The waveguide configuration ofclaim 1 further comprising a third cladding extending about the secondcladding, the third cladding comprising SiO₂ doped with at least one ofB or F.
 6. The waveguide configuration of claim 1 wherein the secondcladding comprises SiO₂ doped with at least one of P and Ge.